Ink jet printheads are useful for printing a wide variety of media (such as paper, certain plastics, cloth, etc.) in a cost effective manner. Printheads have a plurality of nozzles, and which nozzles "fire" is controlled by a computer controller to print the desired images on the media. Each of the nozzles has an effective life that is about the same on any particular printhead, and a printhead has maximum life when all of the nozzles are operated for substantially the same amount of time during the printhead's life. However, in practice when ink jet printheads are used to print repetitive images (such as lines in tables or graphs, logos, etc.) instead of variable images, some nozzles may be used essentially all of the time, and other nozzles hardly at all. This results in the printhead wearing out more quickly than desired, and in fact in extreme cases can result in the printhead no longer being effective to perform its desired function when the majority of the nozzles on the printhead is still completely operable. This problem exists with virtually all types of conventional ink jet printheads, such as (this list being exemplary only) those shown in U.S. Pat. Nos. 4,989,016, 5,640,183, 4,872,026, 4,907,018, and 5,412,410.
One way the above mentioned problem can be addressed is shown in the U.S. Pat. No. 4,989,016 (the disclosure of which is hereby incorporated by reference herein) which controls the nozzles of the ink jet printhead utilizing particular control components so as to shift the print information within acceptable tolerances within the printhead, and thereby even out the life span of the printhead when repetitive work is being performed. However, under some circumstances that technique may not be effective, or may be effective only when combined with other measures.
According to the present invention a method and system are provided which extend the effective life of a printhead when printing repetitive images by utilizing one or a number of different novel techniques to allow which nozzles are being fired to change yet not change the configuration or the position of the repetitive images being printed on the finished media being produced. Basically the techniques that are utilized are one or more of the following (which also may be used in conjunction with the technique in U.S. Pat. No. 4,989,016) when printing media moving with respect to the printhead in a first dimension, at spaced points in time moving the printhead relative to the media in a second dimension (e.g. substantially transverse to the first dimension); at spaced points in time moving the media relative to the printhead in the second dimension; and/or finishing the media after printing to take into account the nozzles that have been fired.
For the purposes of illustration this application refers to ink jet printheads, but it is understood that the principles and methods described herein can be applied equally well to extend the life of printing elements of other print devices, i.e. almost any digital imaging technology. Several digital printing devices use a plurality of individual elements to create the printed image. For example, thermal ink jet (bubble jet) printheads have a plurality of nozzles or orifices, electron beam printers use an ion cartridge with a large number of electron--beam generators, LED electrophotographic printers have arrays of LEDs, and thermal printers use arrays of resistive heating elements. All of the above mentioned printers utilize print elements that wear out with use, just like ink jets. Thus the general term "printhead" as used in this application covers ink jet, thermal ink jet, electron beam, LED, and resistive heating element, and the like, printheads.
According to one aspect of the present invention there is provided a method of printing using at least one printhead (e.g. ink jet) having a plurality of print elements (e.g. LEDs, electron beam generators, resistive heating elements, nozzles), and a media (e.g. paper, plastic sheets or webs, cloths, etc.) that is capable of receiving and holding images (e.g. ink jet) thereon, the method comprising: (a) Moving the media relative to the printhead in a first dimension. (b) Operating the printhead to fire an appropriate first set of the plurality of print elements (e.g. nozzles) thereof to print repetitive images on the media at a desired location thereon while the media is moving relative to the printhead. (c) At spaced points in time moving at least one of the media and the printhead relative to each other in a second dimension, different than the first dimension, to reposition the printhead relative to the media. And (d) in association with (c), adjusting the practice of (b) to fire an appropriate second set of the plurality of print elements (e.g. nozzles), at least some of the second set of print elements (e.g. nozzles) different than the first set, to accommodate the movement in (c) to continue to print the repetitive images on the media at the desired location thereon, so as to extend the effective life of the printhead when printing repetitive images.
In the method (c) may be practiced by moving the printhead only relative to the media, and (a)-(d) are preferably practiced so that the second dimension is substantially transverse to the first dimension. In the method (c) may be practiced to both move the printhead and the media in the second dimension, or only the media. In the method (c) there is further provided (e) at least in part finishing the media after printing to take (d) into account to insure the desired positioning of the repetitive images on the finished media, and there also may be (f) operating the print head to shift print information within acceptable tolerances within the printhead (that is changing the nozzles, etc.) only slightly so that the images and their positions are within acceptable tolerances, as disclosed in U.S. Pat. No. 4,989,016).
In the method (a)-(d) may be practiced to extend the life of some or all of the printheads by at least 10% (e.g. 20-400%) compared to if (c) and (d) were not practiced. The method (a)-(d) may be repeated once or many times depending on the width and distribution of the printing and the number of printing elements in the printhead. A typical scenario is using a 128 nozzle bubble jet ink jet printing cartridge to image one line of 8-point text. This image is approximately 40 pixels in width and is printed by a corresponding 40 nozzles of the printhead. Printing the image at the left, (nozzles 1-40), center (nozzles 42-82) and right (nozzles 84-124) of the printhead will extend the life of the printhead by three times (300%).
In the practice of the method (c) may be practiced at least in part by rotating a detented shaft to advance the shaft at least one detented position, which in turn results in substantially linear movement of the printhead a distance corresponding thereto. Also, (c) may be further practiced so that each detented position of the shaft corresponds to a one pixel substantially linear advance of the printhead, and wherein (d) is practiced to change the nozzles so that the nozzles of the second set are one pixel displaced from the first set. The detented shaft may be rotated manually or automatically.
The at least one printhead may comprise a plurality of printheads and (a)-(d) may be practiced for each of the plurality of printheads that print repetitive images. The printheads may be provided on the same mounting shaft, or different shafts. Also (d) may be practiced to fire a second set of nozzles in which substantially all of the nozzles are different than in the first set; and (c) may be practiced periodically and substantially automatically.
According to another aspect of the present invention there is provided a method of printing using at least one printhead having a plurality of print elements, and a media that is capable of receiving and holding images thereon, said method comprising: (a) Moving the media relative to the printhead in a first dimension. (b) Operating the printhead to fire an appropriate first set of the plurality of print elements thereof to print repetitive images on the media at a desired location on the finished media while the media is moving relative to the printhead. (c) At spaced points in time adjusting the practice of (b) to fire an appropriate second set of the plurality of print elements, at least some of the second set of print elements different than the first set. And (d) finishing the media after printing to take into account (c) so as to ensure that on the finished media the repetitive images are in the desired position, so as to extend the effective life of the printhead when printing repetitive images. In the practice of this aspect of the invention typically the media should be wider than it otherwise would be, so that the finishing equipment can trim various amounts from the different edges thereof to produce a final finished media of the desired configuration.
According to another aspect of the present invention there is provided a system which extends the life of a printhead printing repetitive images. The system may comprise the following components: At least one printhead (e.g. ink jet) having a plurality of print elements (e.g. nozzles). A media that is movable relative to the printhead, and is capable of receiving and holding images (e.g. ink jet) thereon. Means for moving the media relative to the printhead in a first dimension. Means for operating the printhead to fire an appropriate first set of the plurality of print elements thereof to print repetitive images on the media at a desired location thereon. And means for at spaced times moving at least one of the media and the printhead relative to each other in a second dimension, different than the first dimension, to reposition the printhead relative to the media. And wherein the means for operating the printhead is adjusted to fire an appropriate second set of the plurality of print elements different than the first set to accommodate the second dimension movement to continue to print the repetitive images on the media at the desired location thereon, so as to extend the effective life of the printhead (e.g. at least 10%, preferably 20-400% and all narrower ranges within that broad range) when printing repetitive images.
The second dimension moving means may comprise means for moving the printhead, and the second dimension may be substantially transverse to the first dimension. In a preferred embodiment the second dimension moving means comprises a lead screw shaft, a traveling nut mounting the printhead on the lead screw shaft; and a detented shaft connected to the lead screw shaft, rotation of the detented shaft effecting substantially linear movement of the printhead. In the system each detented position of the detented shaft may correspond to substantially linear movement of the printhead one pixel. A knob may be connected to the detented shaft for effecting manual rotation of the detented shaft, or the shaft may be rotated automatically, e.g. by a stepper motor or the like.
It is the primary object of the present invention to provide for the effective utilization of substantially the entire width of a printhead (e.g. ink jet), avoiding the situation where some print elements (e.g. nozzles) are completely worn out while other print elements have a significant part (and sometimes even the majority) of their useful life remaining. This and other objects of the invention will become clear from an inspection of the detailed description, and from the appended claims.